The medium voltage power supply system of nuclear power plant contains various types of cables

with a number of up to hundreds of pieces. It involves a wide range and complex operating environment as well as high single earthing fault probability of the system. The excessive application of a large number of cables will make the capacitive current of the system exceed the standard

causing insulation fault or even arc grounding of the plant power system. There are hundreds of operating conditions of medium voltage auxiliary power system in nuclear power plant. It is in fact impossible to perform grounding current test for all operating conditions. According to the wiring diagram of auxiliary power system in a nuclear power plant in China

a refined grounding current simulation calculation model for multi-cable outgoing with more than 600 pieces of cables is set up. The maximum error between the simulated and measured values of capacitance of cable is 5.5%. Based on this model

the grounding current and system overvoltage under hundreds of operating conditions of medium voltage auxiliary power system are calculated

and the operating conditions of grounding current exceeding the standard are obtained

which can be used to guide the actual operation of nuclear power plant. Then

the real test measurement is performed on the operating conditions of the grounding current exceeding the standard

compared and verified with the simulation results. The maximum error of metal grounding is not more than 4%

and the maximum error of high resistance grounding is not more than 12%. Finally

the suppression measures for the operation conditions of the grounding current exceeding the standard is proposed

which provides a reference for the maintenance and safe operation of cable of the plant power system in the nuclear power plant.